In numerous applications in the electrical art, the resistance needed in circuits are provided by what has become known as thin film resistors. A thin film resistor comprises an insulative substrate and portions of a thin metallic film (which may be a composite film) deposited on the substrate and designed to provide resistance of a preselected value in an electrical circuit. The thin film is deposited on the substrate by vacuum deposition, evaporation, sputtering or other process, and the film has a thickness which is less than one micron. A "thin film" is to be distinguished from "thick films" which have a separate technology, are usually formed by the deposition of pastes or the like on a substrate and have a thickness exceeding 10 microns.
The disclosure hereof regarding thin films is derived in part from the text Thin Film Technology authored by R. W. Berry, P. M. Hall and M. T. Harris and published in 1968 by D. Van Nostrand and Company ("TFT"). Such text and all the references cited therein are incorporated herein by reference.
The thin film elements of thin film resistors are often parts of a much larger thin film pattern produced by well known processes on a substrate to provide thin film integrated circuits each comprising many electric circuit components (such as resistors and capacitors) and conductive leads for coupling the circuit components together. The trend in the manufacture of such integrated circuits has been to miniaturize them insofar as possible in order to realize advantages such as cost and space saving and increased speed of operation of the circuits. The degree however to which such circuits and the electric circuit components thereon can be miniaturized is constrained by limitations in the techniques used to manufacture such circuits. In particular, when a thin film bar resistor is anodized to trim its resistance, size and shape limitations on the smallest mask window usable in the anodizing impose size and shape constraints on the thin film elements of the resistor, and those constraints have, in turn, heretofore limited the minimum resistance obtainable for anodized thin film bar resistors which have been miniaturized insofar as the techniques for manufacturing them will allow. By "an anodized thin film bar resistor" is meant herein a thin film resistor of which the resistance is primarily provided by a rectangular thin film body which has been anodized to trim its resistance.